FIELD OF THE INVENTION
The invention relates to a control for a motor vehicle drive having an automatic transmission, including an engine control through which the torque of the engine is controlled; a transmission control through which the shifting operations of the transmission are controlled and through which the engine control is made to change torque with a tripping signal, which effects a jerk-free shifting operation; and a data exchange between the engine control and the transmission control preceding the tripping signal.
Such a control is used for motor vehicle drives that have automatic transmissions and that have an engine control and a separate transmission control.
An engine control unit in a control system known from German Patent DE 29 35 916 C2, corresponding to U.S. Pat. No. 4,403,527, includes a plurality of performance graphs for various operating states of the engine. Upon initiation of a shifting operation, the transmission control sends the engine control an intervention signal, by means of which a shift from a first to a second performance graph is made. The second performance graph includes reduced values for the engine torque, for instance in order to damp the increase in moment from the engagement of a free-running clutch in the automatic transmission and thus to reduce the jerk or jolt upon shifting or the wear of slipping friction elements in the transmission. The controlled variable for reducing the engine torque is the ignition angle, which is adjusted in the direction of retarding ignition, but the fuel injection quantity may also be reduced.
Upon an adjustment of the ignition angle that is initiated unilaterally by the transmission control, difficulties can arise if the engine control cannot carry out the desired ignition angle adjustment. With a predetermined basic performance graph for determining the ignition angle, for instance, that happens whenever that angle can be adjusted only to a limited extent as compared with the basic value. Such a limitation must be expected above all if the engine control is provided with means for knocking regulation and if that means is active. Its control variable is likewise the ignition angle. Problems can also arise in shifting that takes place in ranges in which there is an increased tendency toward knocking. The tendency toward knocking is in fact even further increased by upshifting. As a rule, activated knocking regulation means cause a power loss, which leads to the desire for more power on the part of the motor vehicle driver and accordingly may cause the driver to downshift again by flooring the gas pedal. The overall result is an unfavorable shifting performance of the automatic transmission. Moreover, in such a case the knocking regulation and the engine intervention by the transmission overlap in an uncontrollable manner.